U.  S.  DEPARTMENT   OF   AGRICULTURE 

OFFICE  OF  EXPERIMENT  STATIONS— FARMERS'  INSTITUTE  LECTURE  NO.  2  (Rev.). 

A.   C.   TRUE,  Director. 


SYLLABUS 


OF 


ILLUSTRATED  LECTURE 


ON 


POTATO  DISEASES  AND  THEIR 
TREATMENT. 


BY 


F.  C.  STEWART,  M.  S.,  and  H.  J.  EUSTACE,  B.  S., 

Agricultural  Experiment  Station,  Geneva,  N.  Y. 


WASHINGTON: 

GOVERNMENT    PRINTING    OFFICE. 

1907. 


736 


U.  S.  DEPARTMENT    OF    AGRICULTURE 

OFFICE  OF  EXPERIMENT  STATIONS-FARMERS'  INSTITUTE  LECTURE  NO.  2  (Rev.). 


A.    C.    TRUE,    Director. 


SYLLABUS 


OF 


ILLUSTRATED  LECTURE 


ON 


POTATO  DISEASES  AND  THEIR 
TREATMENT. 


BY 


F.  C.  STEWART,  M.  S.,  and  H.  J.  EUSTACE.  B.  S., 

Agricultural  Experiment  Station,  Geneva,  N.  Y. 


WASHINGTON: 

GOVERNMENT    PRINTING    OFFICE. 
1907. 


PREFATORY  NOTE. 


This  syllabus  of  a  lecture  upon  Potato  Diseases  and  Their  Treat- 
ment, by  F.  C.  Stewart,  M.  S.,  Botanist,  and  II.  J,  Eustace,  B.  S., 
Assistant  Botanist,  of  the  New  York  Agricultural  Experiment  Station, 
Geneva,  N.  Y.,  is  accompanied  by  47  views  illustrating  methods  for 
controlling  potato  diseases.  The  syllabus  and  views  have  been  pre- 
pared for  the  purpose  of  aiding  farmers'  institute  lecturers  in  their 
presentation  of  this  subject  before  institute  audiences. 

The  numbers  in  the  margins  of  the  pages  of  the  syllabus  refer  to 
similar  numbers  on  the  lantern  slides  and  to  their  legends  as  given  in 
the  Appendix;  those  in  the  body  of  the  text  refer  to  corresponding 
numbers  in  the  list  of  authorities  and  references,  page  29. 

In  order  that  those  using  the  lecture  may  have  opportunity  to  fully 
acquaint  themselves  with  the  subject,  references  to  its  recent  literature 
are  given  in  the  Appendix. 


John  Hamilton, 
Farmers*  Institute  Specialist. 


Recommended  for  publication. 
A.  C.  True,  Director. 


Publication  authorized. 

James  Wilson,  Secretary  of  Agriculture. 

Washington,  D.  C,  October  i,  190b. 

(2) 


POTATO  DISEASES  AND  THEIR  TREATMENT. 


By  F.  C.  Stewart,  M.  8.,  and  H.  J.  Eustace,  B.  S. 


INTRODUCTION. 

View. 

For  the  most  part  farmers  recognize  but  three  potato  dis- 
eases, namely,  blight,  rot,  and  scab.  The  first  important  fact 
to  be  stated  is  that  there  are  several  kinds  of  potato  blight, 
and  treatment  which  prevents  one  kind  of  blight  may  be 
entirely  worthless  for  another  kind.  Likewise,  there  are 
different  kinds  of  potato  rot.  Unfortunately,  these  blights 
and  rots  are  often  difficult  to  distinguish  without  the  aid  of  a 
microscope.  Farmers  can  scarcely  expect  to  be  able  always 
to  identify  them  with  certainty,  but  it  is  worth  while  to  learn 
the  leading  symptoms  of  the  principal  diseases  in  order  that 
rational  methods  of  treatment  may  be  employed.  Doubtful 
cases  may  be  referred  to  the  State  experiment  station. 

PRINCIPAL  DISEASES. 

Early  Blight.  la — A  widespread  disease,  probably  more  ^ 
destructive  in  the  aggregate  than  late  blight.  Attacks  chiefly 
the  leaves,  sometimes  also  the  stems,  but  never  the  tubers. 
Appears  in  the  form  of  dead,  brown  spots  irregularly  distrib- 
uted over  the  leaf,  but  most  numerous  around  the  margins 
and  in  portions  mutilated  by  insects.  The  larger  spots  show 
concentric  rings  often  described  as  "  target-board"  markings. 
Spots  frequently  coalesce  and  form  large  areas  of  dead  tissue.  2 
In  the  later  stages  the  dry  tips  and  margins  of  the  leaves  may 
roll  up  as  in  tip  burn.  Disease  ma}^  appear  at  any  time  after 
the  plants  are  6  inches  high,  the  older  leaves  being  attacked 
first.  The  virulence  of  the  disease  increases  with  the  age  of 
the  plants.  Because  of  its  slow  progress  it  is  regarded  by 
many  farmers  as  the  natural  ripening  of  the  plants.  Probably 
it  often  reduces  the  yield  by  as  much  as  25  to  50  bushels  per 

«  Numbers  refer  to  list  of  references  on  p.  29. 
(3) 


acre  without  attracting  attention.  Plants  suffering  from 
drought,  insufficient  food,  flea-beetle  attack,  or  any  thing  else 
tending  to  reduce  their  rigor,  are  especially  liable  to  attack. 
Early  blight  is  caused  by  the  parasitic  fungus  AUernaria  solani. 
It  may  he  largely  prevented  by  spraying  with  Bordeaux  mix- 
ture. 

Tii-  Hi  i:\.  A  common  trouble  often  confused  with  early 
blight  The  tips  and  margins  of  the  have-  dry,  blacken, and 
roll  up.  Spots  with  "target-board"  markings  also  may 
occur  on  interior  of  old  leaves.  Disease  most  troublesome  as 
plant-  approach  maturity.  Caused  primarily  by  dry,  hot 
weather  and  lack  of  water  in  the  soil.  Aggravated  by  attacks 
of  insects,  particularly  flea-beetles,  the  punctures  of  which 
greatly  increase  the  loss  of  water  from  the  leaves;  also  by 
injury  to  the  roots  through  too  deep  cultivation  late  in  the 
season.  Potatoes  grown  on  light,  sandy  soil  are  especially 
liable  to  tip  burn. 

With  regard  to  the  prevention  of  tip  burn.  Prof.  L.  H. 
Jones,  an  authority  on  the  subject,  say-: 

Effort  should  be  made  to  increase  and  sustain  the  general  vigor  of  the 
plant  by  proper  selection  of  varieties,  preparation  and  cultivation  of  the 
soil,  and  protection  against  the  attacks  of  insects  and  fungi.  The  only  thing 
that  can  be  done  in  addition  is  to  irrigate  in  times  of  extreme  drought. 
*  *  *  In  the  Eastern  States  proper  attention  to  the  accumulation  of  a 
store  of  humus  in  the  soil  by  the  more  frequent  growth  of  clover,  etc.,  will 
do  much  to  reduce  injuries  from  tip  burn.  Such  preparation  of  the  soil, 
with  more  frequent  tillage  during  periods  of  drought,  and  proper  spraying 
with  Bordeaux  mixture,  will  reduce  the  damage  to  a  thing  of  little  practical 
importance. 

Sun  Scald.* — Sun  scald  is  considered  by  some  pathologists 
as  a  form  of  tip  burn.  When  a  long  period  of  cloudy,  wet 
weather  is  immediately  followed  by  several  hot,  bright  days, 
potato  foliage  may  be  injured  by  sun  scald.  The  tips  and  mar- 
gins of  the  younger  leaves  suddenly  turn  brown  and  dry  up  as 
in  tip  burn.  Leaves  grown  in  cloudy,  damp  weather  are  tender, 
and  too  readily  lose  their  water  by  evaporation  when  exposed 
to  the  sun.  The  extent  of  the  damage  done  by  sun  scald  is 
uncertain,  but  it  is  probably  not  great.  Its  symptoms  are  so 
similar  to  those  of  tip  burn  that  it  is  impossible  to  distinguish 
the  two  diseases  except  in  the  early  stages  and  when  the 
weather  conditions  are  known. 

Paris-green  Injury.5 — Paris  green  is  now  quite  generally 
used  on  potatoes  to  prevent  the  ravages  of  the  Colorado 
potato  beetle  and  other  insects  which  feed  on  the  foliage. 
When  properly  applied  with  limewater  or  Bordeaux  mixture 


View. 

and  in  moderate  amount  (8  ounces  to  1  pound  in  50  gallons 
of  water),  it  is  entirely  harmless  to  potato  foliage.  But  it  is 
an  undeniable  fact  that  its  use  by  farmers  frequently  results 
in  considerable  damage.  Many  cases  of  supposed  blight  are 
nothing  but  Paris-green  injury. 

The  symptoms  of  Paris-green  injury  are  very  similar  to 
those  of  early  blight.  Dead  brown  spots  appear  on  the  leaves. 
Even  the  target  markings  are  sometimes  seen.  Injury  is 
most  likely  to  occur  where  the  tissue  has  been  mutilated  by 
insects,  as,  for  example,  around  flea-beetle  punctures.  Leaves 
with  unbroken  epidermis  are  not1  often  affected. 

Paris  green,  as  found  on  the  market,  varies  somewhat  in 
chemical  composition.6  Its  poisoning  properties  are  mainly 
due  to  the  arsenic  it  contains.  Most  of  the  arsenic  is  in  the 
form  of  compounds  insoluble  in  water,  but  there  is  almost 
always  present  a  small  amount  of  soluble  arsenic  compounds. 
It  is  the  water-soluble  arsenic  that  causes  injury  to  foliage, 
and  the  less  there  is  of  it  the  better.  In  some  States  this  is 
regulated  by  law.  In  New  York  legal  Paris  green  must  not 
contain  more  than  3£  per  cent  of  soluble  arsenic  compounds. 

The  remedy  for  this  trouble  lies  in  the  use  of  an  equal  quan- 
tity of  lime  with  the  Paris  green.  With  lime  the  soluble 
arsenic  forms  insoluble  arsenite  of  lime  which  is  harmless  to 
foliage.  When  Paris  green  is  used  with  Bordeaux  mixture 
the  lime  in  the  Bordeaux  neutralizes  the  soluble  arsenic,  and 
injury  to  the  foliage  is  thus  prevented.  To  insure  safety 
Paris  green  should  be  used  only  with  limewater  or  with  Bor- 
deaux. If  used  in  dry  form  air-slaked  lime  should  be  mixed 
with  it. 

London  purple  and  other  arsenical  poisons  containing  water- 
soluble  arsenic  compounds  produce  injury  similar  to  that  made 
by  Paris  green,  and  should  invariably  be  applied  with  lime- 
water  or  Bordeaux. 

It  should  also  be  stated  that  many  farmers  use  Paris  green 
in  excessive  amount.  This  is  not  only  wasteful,  but  the  dan- 
ger of  injury  to  the  foliage  is  unnecessarily  increased.  One 
pound  per  acre  evenl}<  distributed  is  entirely  sufficient  to  con- 
trol Colorado  potato  beetles,  or  "bugs"  as  they  are  called.7 

Late  Blight  and  Rot.8 — This  form  of  blight  makes  its 
appearance  during  warm,  moist  ("muggy  ")  weather  in  August 
and  September.  It  may  occur  on  earlypotatoes  in  Jul}',  but 
it  is  chiefly  destructive  to  late  potatoes  during  the  last  month 
of  their  growth.     Hence  the  name  late  blight. 


It  tir-t  appears  od  the  leaves  (usually  the  lower  ones)  in  the 

5  form  of  BmaU  In-own  spots  which  rapidly  enlarge.    On  the 

under  surface  the  margins  of  the  diseased  spots  are  covered 

with  a  tine  frost-like  mildew.  In  moist,  cloudy  weather  this 
mildew  i-  easily  seen,  hut  on  a  dry  day  it  may  be  difficult  to 
detect.  Affected  Leaves  soon  die.  Under  favorable  condi- 
tions the  disease  progresses  with  astonishing  rapidity.     A  tine 

field  of  potatoes  may  he  completely  ruined  in  a  few  day-  after 

<>  the  first  appearance  of  the  disease.     Plants  in  the  advanced 

stage  of  the  disease  have  onlv  small  tufts  of  green  leai 

the  tips  of  the  stalk-.  Afostof  the  leave-  hang  blackened  and 
shriveled  as  if  scorched  by  lire.  Blighted  fields  emit  a  strong 
odor,  particularly  when  the  foliage  i-  wet. 

Contrary  to  popular  opinion  this  blight  is  not  caused  by 

7  wet  weather.  The  real  cause  is  a  parasitic  fungus,  PhytopK- 
thora  infegtans.  Without  the  fungus  there  could  be  no  blight 
of  this  kind,  no  matter  what  the  weather  might  be.  Blight  is 
most  virulent  in  wet  weather  simply  because  the  blight  fun- 
gus thrives  best  and  spreads  most  rapidly  in  wet  weather. 

The  frost-like  mildew  on  the  under  surface  of  the  diseased 
spots  is  composed  of  minute,  branching,  tree-like  affairs. 
These  are  the  spore-stalks  of  the  fungus.  At  the  end  of 
branch  there  is  a  minute  egg-shaped  body — a  spore.  When 
a  spore  falls  upon  a  healthy  potato  leaf  in  a  drop  of  water  it 
germinates  in  a  few  hours  and  forces  a  slender,  colorless  thread 
into  the  tissue  of  the  leaf.  Once  within  the  leaf  the  colorless 
thread  branches  many  times  and  penetrates  the  leaf  in  all 
directions,  absorbing  nourishment  from  the  cells  of  the  leaf 
and  later  killing  them.  As  the  leaf  tissue  dies  the  fungus 
forms  spore-stalks  bearing  new  spores,  and  the  life  cycle  is 
complete.  Usually  four  or  rive  days  elapse  between  the  germ- 
ination of  the  spores  and  the  production  of  a  new  crop  of 
spores.     Hence  the  rapidity  with  which  the  disease  spreads. 

8  Late  blight  may  or  may  not  be  followed  by  rot  of  the 
tubers,  according  to  soil  and  weather  conditions.  Rot  is  worse 
in  wet,  heavy  soils  (clay  and  loam)  than  in  sandy  soil.  When 
rot  occurs  it  is  due  to  -pores  from  the  blighted  plants,  which 
fall  upon  the  ground  and  are  washed  down  to  the  tubers  by 
rain.  Sometimes  the  fungus  passes  down  the  stem  to  the 
tubers,  but  this  method  of  infection  is  the  exception  rather 
than  the  rule. 

The  potato  blight  has  no  spores  which  live  over  winter.     It 
is  believed  to  pass  the  winter  in  the  tissue  of  slightly  affected 


View. 

tubers.     Hence  the  inadvisability  of  planting  tubers  showing 
signs  of  rot.9 

In  America  late  blight  is  destructive  chiefly  in  the  north- 
eastern United  States  and  Canada.  In  the  South  and  West  it 
is  not  common.  It  is  estimated  that  in  New  York  the  loss 
from  late  blight  in  1903  amounted  to  50  bushels  per  acre  on 
the  average.10  In  Vermont  the  loss  is  often  much  greater 
than  this.11  The  virulence  of  the  disease  varies  much  from 
year  to  year  with  the  weather  conditions,  always  being  great- 
est in  wet  seasons.  Late  blight  may  be  prevented  by  thor- 
ough and  frequent  spraying  with  Bordeaux  mixture. 

Bacterial  Wilt  and  Wet  Rot.12 — Characterized  by  a  9 
sudden  wilting  of  the  plants,  followed  by  a  wet  rot  of  the 
tubers.  Caused  by  bacteria  {Bacillus  solanacearum).  Infec- 
tion probably  occurs  both  above  and  below  ground.  Spread 
largely  by  leaf-eating  insects.  Same  disease  attacks  tomatoes 
and  egg  plants.  Destructive  chiefly  in  the  South.  The  ex- 
tent of  its  ravages  in  the  North  is  uncertain,  but  probably 
considerable.  The  rot  caused  by  it  is  often  confused  with 
that  caused  try  the  late-blight  fungus. 

Dry  Rot.13 — Attacks  all  parts  of  the  plant  below  ground —  10 
tubers,  tuber  stems,  roots,  and  lower  portion  of  the  stem. 
The  first  indication  of  trouble  is  seen  in  the  curling  and  roll- 
ing of  the  leaves,  which  at  the  same  time  become  paler  green 
than  normal.  This  symptom  may  occur  at  any  time  after  the 
plants  are  a  foot  high.  It  is  followed  by  gradual  drying  up 
and  premature  death  of  the  plant.  When  first  dug  the  tubers 
of  affected  plants  appear  sound,  and  are  often  marketed  with- 
out the  disease  being  detected.  But  when  cut  across  at  the  H 
stem  end  there  is  seen  a  ring  of  black  or  brown  streaks  ex- 
tending from  the  stem  into  the  flesh.  This  is  the  most  reliable 
symptom.  Hence  disease  is  sometimes  called  bundle  black- 
ening. So  long  as  they  are  in  the  ground  the  tubers  do  not 
rot,  but  in  storage  the  blackening  of  the  tissue  increases  and 
ultimately  many  of  the  tubers  become  shriveled  up  with  dry 
rot.  Frequently  one  end  of  the  tuber  is  dry  rotten  while  the 
other  end  remains  sound.  Because  of  this  peculiarity  the 
disease  is  often  called  dry  end-rot.  12 

The  cause  of  dry  rot  is  a  fungus  (Fusarium  oxyspmtim),  the     13 
feeding  threads  of  which  occur  abundantly  in  the  diseased 
tissue  of  stem,  roots,  and  tubers,  being  especially  conspicuous 
in  spring  on  the  rotten  tubers,  where  it  appears  in  the  form 
of  dense,  whitish  tufts  breaking  through  the  skin. 


8 

Vieu 

Dry  rot  seems  to  be  common  throughout  the  United  States, 
but  it  has  been  bo  much  confused  with  other  forms  of  blight 

and  rot  that  the  amount  of  damage  done  by  it  is  difficult  to 
estimate. 

J  4  &  ah." —  Found  only  on  the  tubers;   never  attacks  the  tops; 

almost  too  well  known  to  need  description.  The  skin  of  the 
tulxM-  becomes  roughened,  pitted,  and  cracked  in  various 
Ways.      A  widespread  and  destructive  (Usee 

During  the  past  fifty  year-  scab  ha-  been  studied  by  many 

investigators,  and  many  theories  as  to  it>  cause  have  been 
advanced.11  It  is  now  believed  that  scab  may  he  due  to  dif- 
ferent causes,  hut  that  by  far  the  greater  part  of  the  trouble 
in  this  country   is  caused    by  a   parasitic   fungus  (Oospora 

scabies).  The  scab  ulcers  often  become  a  lodging  place  for 
various  species  of  fungi  and  insects,  which  feed  upon  the 
dead  tissue  and  in  some  cases  extend  the  injury. 

Our  knowledge  of  the  true  nature  of  potato  scab  rests 
chiefly  upon  the  investigations  in  1890  of  Dr.  R.  Thaxter  w 
at  the  Connecticut  Experiment  Station.  He  discovered  the 
fungus  Oospora  scabies,  and  by  artificially  inoculating  glow- 
ing tubers  with  pure  cultures  of  it  proved  it  to  be  the  cause 

15  of  scab.  In  one  case  he  applied  some  of  the  fungus  to  the 
surface  of  a  tuber  in  the  form  of  his  monogram.  "R,  T." 
This  was  done  without  injury  to  the  skin,  and  yet  in  about 
three  weeks  scab  appeared  wherever  the  fungus  had  been 
applied  and  nowhere  else. 

The  scab  fungus  lives  from  year  to  year  in  the  soil.  It  is 
spread  chiefly  by  means  of  diseased  tubers  used  for  seed.  Iry 
the  washing  of  soil,  and  on  tools  used  in  cultivation:  also  in 

16  manure  from  animals  fed  on  scabby  potatoes.  The  beet 
often  sutlers  from  scab  caused  by  the  same  fungus,  and  it  is 
suspected  that  the  turnip  and  some  other  plants  are  occasion- 
ally attacked  by  it.17 

Rhizoctonia,18  Rosette,  and  "Little  Potatoes." — 
Rhizoctonia  is  a  fungus  often  found  on  the  underground 
parts  of  various  plants.  In  some  cases  it  i-  parasitic  and 
destructive:  for  example,  stem  rot  of  carnation,  rot  of  green- 
house lettuce,  and  root  rot  of  beets.  In  many  other  cases  it 
appears  to  be  but  little  if  at  all  injurious  to  the  plants 
infested  by  it.  There  are  different  kinds  or  species  of 
Rhizoctonia.  but  how  many  is  not  known.  The  one  infesting 
the  carnation  is  the  same  as  that  on  the  beet,  but  different 
from  the  one  on  lettuce.  In  Europe  Rhizoctonia  solani  is 
believed    to    cause    a    rot  of   potato  tubers.      In   the   United 


9 

View. 

States  a  species  of  Rhizoetonia  occurs  abundantly  on  potato 
tubers  and  stems.  In  appearance  it  is  very  similar  to  the 
European  R.  sola?ii,  but  it  does  not  rot  the  tubers  and  is  not 
often  seriously  injurious  to  the  plants  in  any  way.  This  is 
our  opinion.  Some  other  plant  pathologists  think  differently. 
It  is  apparently  the  cause  of  a  serious  disease  in  the  South, 
and  in  the  Middle  and  Western  States,  but  does  little  harm  in 
the  Northeastern  States. 

Selby,19   of   Ohio,    has   described   a   prevalent  disease   of      17 
potatoes  in  that  State  which  he  calls  "rosette."     It  is  charac- 
terized by  stunted  growth,  clustering  of  the  leaves  in  rosettes, 
and  premature  death  of  the  plants.     He  attributes  the  trouble 
to  Rhizoetonia. 

Rolfs,20  of  Colorado,  believes  Rhizoetonia  to  be  one  of  the 
principal  causes  of  failure  with  potatoes  in  some  parts  of 
Colorado.  He  says  it  attacks  the  tuber  stems,  also  girdles 
the  main  stem  underground,  thereby  causing  the  develop- 
ment of  an  abnormally  large  top  and  a  cluster  of  small  potatoes 
at  the  surface  of  the  soil.  This  trouble  is  known  as  "little 
potatoes." 

On  the  tubers,  Rhizoetonia  forms  compact  brown  bodies  18 
called  sclerotia.  They  are  irregular  in  outline  and  vary  in 
size  from  a  mere  speck  to  the  size  of  a  half  pea.  When  dry 
they  are  dirt-colored  and  difficult  to  detect,  but  when  wet 
thej  are  dark  brown  and  easily  seen.  They  adhere  firmly 
and  are  difficult  to  remove  by  washing.  Many  housekeepers 
are  familiar  with  them.  The  feeding  threads  (hypha?)  found  19 
on  potato  stems  are  rather  coarser  than  is  usual  with  fungi, 
nearly  colorless  when  young,  but  brown  when  old.  The 
sclerotia  are  composed  of  short,  thick,  brown  cells,  closely 
packed  together. 

Internal  Browning.31 — Occasional^  found  in  various  parts 
of  the  United  States,  but  not  an  important  disease.  Out- 
wardly the  tubers  appear  sound,  but  when  cut  disclose  numer- 
ous irregular  rust-brown  spots  scattered  through  the  flesh. 
Although  affected  tubers  do  not  rot  they  are  unfit  for  table 
use.  Both  cause  and  remedy  are  unknown.  Diseased  tubers 
will  grow  and  produce  a  fair  crop  which  may  be  free  from 
disease,  but  the  use  of  such  seed  is  inadvisable. 

PRINCIPAL  INSECT  ENEMIES  OF  POTATO  FOLIAGE. 

Introduction. — A  few  of  the  principal  insects  which  feed 
upon  potato  foliage  are  briefly  discussed  here,  for  the  reason 
that  their  ravages  are  often  intimately  associated  with  certain 

28620— No.  2—07 2 


10 


View. 


forme  of  blight,  and  treatment  for  them  may  be  profitably 
combined  with  the  treatment  for  blight. 

20  Colorado  Potato  Beetle,  The  large  yellow  and  black 
-i  riped  beetles,  commonly  called  "  bugs,"  arc  too  common  and 
well  known  to  need  description.  This  insect  has  migrated  from 
the  West  to  the  East.  In  the  Eastern  State-  it  i-  the  Leading 
insect  pot  of  the  potato. 

21  Blister  Bebtli  Several  species  of  blister  beetle-  feed 
on  potato  foliage,  frequently  doing  much  damage,  particu- 
larly in  the  Mississippi  Valley.  They  are  -lender,  rather 
soft-bodied  beetles,  about  one-half  inch  long.  The  two  species 
most  troublesome  to  potatoes  are  a  black  one  and  an  ash-gray 
one.  They  are  very  active,  flying  readily  when  disturbed. 
They  usually  appear  suddenly  in  swarms.  The  larvae  feed  on 
grasshopper  eggs. 

22  Flea-Beetles.23 — These  are  small,  black  jumping  beetle- 
about  one-twelfth  inch  in  length,  which  eat  minute  round 
holes  in  the  leaves.  Being  so  small  and  very  shy  they  are 
often  overlooked,  even  when  numerous  enough  to  do  damage. 
They  are  most  troublesome  on  sand}r  soil.  Frequently  they 
do  an  enormous  amount  of  damage,  particularly  in  dry 
weather,  when  the  breaking  of  the  epidermis  in  so  many 
places  causes  the  leaves  to  lose  water  rapidly  and  dry  up. 
Moreover  their  punctures  serve  as  a  starting  point  for  Paris 
green  injury  and  offer  an  easy  entrance  to  the  early  blight 
fungus.  Flea-beetles  may  attack  the  plant  at  any  time,  but 
in  the  Northern  States  are  usually  most  numerous  and 
destructive  about  August  1.  The  larvae  feed  on  potato  roots 
and  tubers,  occasionally  causing  a  trouble  known  as  "pimply 
potatoes."24 

SPRAYING  TO  PREVENT  BLIGHT,  ROT,   AND  INSECT 
RAVAGES.25 

Introduction. — Having  described   the  principal  disc: 
and  insects  affecting  the  potato,  let  us  now  take  up  the  sub- 
ject of  methods  of  combating  them.     One  of  the  most  impor- 
tant lines  of  treatment  is  that  of  spraying,  which  we  will 
consider  first 

Since  about  1888  it  has  been  known  that  the  ravages  of  late 
blight  may  be  prevented  by  spraying  with  Bordeaux  mix- 
ture.20 This  has  been  settled  beyond  all  doubt.  More 
recently  numerous  experiments  have  shown  that  Bordeaux 
mixture  is  beneficial  to  potatoes  in  other  ways.  viz.  it  pre- 

23  vents  early  blight,27  greatly  reduces  the  damage  done  by  flea- 


11 

View. 

beetles,28  makes  it  possible  to  more  thoroughly  control  Colo-    24 
rado  beetles,29  blister  beetles,  and  grasshoppers,30  prevents    25 
danger  of  Paris-green  injury,  and  stimulates  the  plants  to    26 
better  growth  and  larger  yield,  even  when  diseases  and  insects 
are  absent.31 

Materials,  Methods,  and  Machinery. — Several  fungi- 
cides have  been  tested  and  Bordeaux  mixture  found  to  be  the 
best  of  all.32  Use  Bordeaux  mixture  made  by  the  following 
formula:  (1)  6  pounds  copper  sulphate33  (blue  vitriol)  dis- 
solved in  25  gallons  of  water;  (2)  4  to  6  pounds  stone  lime, 
slaked  as  for  whitewash,  then  diluted  with  water  to  20  or  25 
gallons;  (3)  mix  1  and  2,  stirring  thoroughly.  Use  while 
fresh. 

The  quality  of  Bordeaux  depends  largely  upon  its  method 
of  preparation.    The  best  Bordeaux  is  that  which  settles  most 
slowly.     It  is  believed  that  Bordeaux  mixtures  which  settle 
quickly  are  less  efficient  because  they  do  not  adhere  so  well      27 
and  are  more  difficult  of  uniform  distribution.    The  best  Bor-      28 
deaux  is  made  by  using  cold  dilute  solutions,  uniting  them      29 
quickly  and  stirring  thoroughly.3*    (For  further  details  of  the 
preparation  of  Bordeaux  mixture,  see  Appendix,  II,  page  23.) 

Whatever  poison  is  used  for  insects  may  be  mixed  with  the 
Bordeaux  and  applied  at  the  same  time.  When  both  economy 
and  efficiency  are  considered,  the  best  two  poisons  for  use 
with  Bordeaux  on  potatoes  are  Paris  green  and  arsenite  of 
soda.  The  latter  is  considerably  the  cheaper,  but  is  some 
trouble  to  prepare.  (For  method  of  preparation,  see  Appen- 
dix, III,  page  25.) 

The  quantity  of  poison  to  use  with  50  gallons  of  Bordeaux 
depends  on  the  acreage  to  be  covered.  One  pound  of  Paris 
green,  or  its  equivalent,  in  arsenite  of  soda  is  sufficient  for  an 
acre.  Hence,  if  50  gallons  are  applied  to  1  acre,  use  with  it 
1  pound  of  Paris  green;  if  applied  to  2  acres,  use  2  pounds  of 
Paris  green.  Korse  sprayers  having  one  nozzle  per  row 
apply  from  25  to  40  gallons  per  acre.  Paris  green  applied 
with  Bordeaux  is  more  effective  than  when  used  alone,  because 
it  is  more  evenly  distributed  and  adheres  better.  Moreover, 
Bordeaux  itself  is  a  deterrent  to  insects,  being  very  distasteful 
to  them. 

The  number  of  applications  and  the  time  of  making  them 
will  vary  somewhat  according  to  weather  conditions,  the 
prevalence  of  insects  and  disease,  and  thoroughness  of  the 
spraying.  As  a  general  rule,  commence  spraying  when  the 
plants  are  6  to  8  inches  high,  and  repeat  the  treatment  at 


L2 


30 


31 


32 


33 


34 


intervals  of  ten  to  fourteen  days  as  long  as  the  plants  continue 
green.*1  This  requires  five  or  >ix  applications  during  "the 
season.  In  no  case  Bhould  the  first  spraying  be  postponed 
longer  than  the  time  of  the  first  appearance  of  "bugs"  in 
destructive  numbers.     At  such  time  poison  must  be  applied 

anyway  to  kill  the  "bugs,"  and  it  is  but  little  extra  expense 
to  use   Bordeaux  with  it  and  secure  the   protection   it  affords. 

For  late  blight  the  later  sprayings  are  the  most  important. 
In  fact,  protection  against  late  blight  and  its  rot  can  be 
secured  by  three  thorough  sprayings,  making  the  first  during 

the  blossoming  period  and  the  other  two  at  intervals  of  about 
two  weeks. 

From  the  blossoming  period  on,  the  plants  should  be  kept 
constantly  covered  with  Bordeaux  mixture.  Should  rain  come 
immediately  after  spraying  before  the  mixture  has  dried  the 
work  should  be  done  over  at  once.  (See  Appendix,  V,  page  26.) 
It  is  in  wet  weather  that  spraying  should  be  most  frequent  and 
thorough,  because  late  blight  is  most  active  then  and  much  of 
the  mixture  is  washed  off  by  rain. 

The  kind  of  sprayer  to  use  depends  chiefly  upon  the  area  to 
be  sprayed.  For  gardens  and  fields  of  1  acre  or  less,  com- 
pressed-air sprayers  holding  3  to  5  gallons  and  costing  from 
$3  to  $8  answer  very  well.  There  are  also  bucket  pumps 
which  may  be  had  for  the  same  price  and  which  are  quite 
isfactory.  Likewise  the  knapsack  sprayers  to  be  carried  on 
the  back  are  useful  for  small  areas,  but  the}'  cost  $10  to  $15. 
One  of  these  small  hand  sprayers  is  very  generally  useful 
about  the  garden  and  grounds  for  applying  insecticides  and 
fungicides  to  small  trees  and  shrubs  as  well  as  to  potatoes  and 
other  vegetables. 

When  it  is  desired  to  use  the  same  outfit  for  spraying  in  the 
potato  field  and  in  the  orchard,  a  barrel  spray-pump  outfit 
(cost  $10  to  $20)  is  the  proper  thing  to  use.  In  the  potato 
field  this  outfit  may  be  used  in  two  ways:  First,  it  may  be 
drawn  through  the  field  in  a  Light  wagon  or  two-wheeled  cart, 
with  a  man  to  pump  and  drive  while  two  others  walk  and 
direct  the  spray  nozzles.  This  method  requires  much  man 
labor  and  is  therefore  expensive,  but  no  extra  outlay  for 
apparatus  is  necessary  and  the  Bpraying  can  be  done  more 
thoroughly  than  by  any  other  method  practical  in  large  fields. 
Second,  it  may  be  used  on  a  one-horse  two-wheeled  cart,  hav- 
ing at  the  rear  about  '.*  feet  of  f-inch  iron,  or,  better  still, 
bra--  pipe,  communicating  with  the  pump  by  means  of  a 
short  piece  of  hose.     To  this  pipe  eight  -pray  nozzles  itwo  for 


13 


Total 55. 


The  total  cost  per  acre  for  5  sprayings  was  $4.     Seven 
rows  800  feet  long  were  left  unsprayed,  but  were  kept  free 


i  u " . 


each  row)  are  attached  in  pairs.  One  man  pumps  and  drives, 
spraying  four  rows  at  each  passage.  All  things  considered, 
this  is  the  most  satisfactory  potato-spraying  outfit  yet  devised. 
It  can  be  built  at  a  cost  of  $30  to  $40. 

For  large  fields  of  10  or  more  acres  geared  pumps  operated  35 
by  horsepower  arc  entirely  practical.  Several  good  outfits 
of  this  kind  are  on  the  market.  Their  chief  advantage  over 
the  barrel  outfit  last  mentioned  is  that  the  labor  of  pumping 
is  shifted  from  the  driver  to  the  horse.  They  have  the 
disadvantage  in  being  more  expensive  ($60  to  $100),  less 
durable,  and  of  heavier  draft. 

Of   spray  nozzles   there  are  many  kinds.     For   spraying      36 
potatoes  Vermorel  nozzles  are  best.     They  can  be  obtained 
from  most  manufacturers  of  spraying  machinery. 

Does  Spraying  Pay? — Spraying  rnay   or   may   not   pay 
according  to  circumstances.     In  some  localities  and  in  some 
seasons  it  is  more  profitable  than  in  others.     In  the  northeast- 
ern United  States,  where  late  blight  is  often  destructive,  the 
increase  in  }neld  due  to  spraying  is  f  requently  enormous.     At 
the  Vermont  Experiment  Station  the  average  increase  in  yield 
due  to  spraying  during  fifteen  consecutive  seasons  (1891-1905)       **  ' 
was  119  bushels  per  acre.     The  greatest  gain  was  in  1893,       38 
when  it  was  224  bushels  per  acre,  and  the  least  in  1900,  when       39 
it  was  60  bushels.30     At  the  New  York  Experiment  Station      40 
the  average  gain  from  five  to  seven  sprayings  during  five 
consecutive  seasons  (1902-1906)  was   132   bushels  per  acre. 
Perhaps  farmers  may  not  be  be  able  to  duplicate  these  results, 
but  they  show  what  is  possible. 

In  1903  J.  V.  Salisbury  &  Sons,  Phelps,  N.   Y.,  made  an 
experiment 37  which  throws  much  light  on  the  subject  under 
discussion.     They  sprayed  14  acres  of  late  potatoes  five  times      4J 
with  a  2-horsepower  sprayer,  which  sprays  5  rows  at  each       42 
passage.     A  record  was  kept  of  all  expense  of  the  spraying,       43 
the  items  being  as  follows: 

504  pounds  copper  sulphate,  at  6  cents $30.  24 

8  bushels  lime,  at  35  cents 2.  80 

12  pounds  white  arsenic,  at  5^  cents 66 

55  hours  labor  for  man,  at  1 Ih  cents 9.  63 

47  hours  labor  for  team,  at  17£  cents 8.  23 

Wear  on  sprayer 4.  20 


44 


14 


of  bugs  by  application  of  Paris  green.  In  the  fall  th< 
row-  were  dug  separately  and  weighed,  aa  were  also  7  spn 
rows  adjacent  The  yield  of  the  unsprayed  rows  was  at  the 
rate  of  38  bushels  per  acre,  and  of  the  sprayed  rows  147 
bushels.  Thus  there  was  ■  gain  of  64  bushels  of  marketable 
tubers  per  acre,  worth,  at  time  of  digging,  .'»' I  oenta  per 
bushel,  or  S*3-2.  Deducting  the  cost  of  spraying,  there  is  left 
a  net  profit  of  138  per  acre,  or  a  total  of  $392  on  the  14  m 

There  was  uo  loss  from  rot  even  on  the  nnsprayed  row-. 
The  gain  on  the  sprayed  row-  was  due  ohiefly  to  the  preven- 
tion of  late  blight,  thereby  prolonging  the  life  of  the  plants 
fully  three  weeks. 

Of  course  it  is  true  that  late  blight  was  exceptionally  severe 
in  New  York  in  1903,  and  such  results  as  these  van  not  be 
obtained  every  season:  but  it  should  be  noted  that  in  this  one 
season's  work  Messrs.  Salisbury  made  enough  money  to  spray 
the  same  acreage  in  potatoes  during  the  next  six  years  with- 
out loss,  even  if  no  increase  in  yield  is  obtained  during  that 
time.  In  other  words,  the  crop  is  insured  against  "  bugs'' 
and  blight  for  six  years. 

During  four  seasons  (1903-1906)  the  New  York  State 
Experiment  Station  cooperated  with  farmers  in  making  busi- 
ness experiments  like  the  above.  Forty -eight  such  experi- 
ments were  made.  The  average  increase  in  yield  due  to 
spraying  was  52  bushels  per  acre  and  the  average  net  profit 
$20.56  per  acre.  The  same  station  has  gathered  the  results 
of  150  volunteer  experiments  made  by  New  York  farmers 
during  three  seasons  (1904-1906)  and  tinds  the  average  gain 
from  spraying  to  be  56  bushels  per  acre. 

Some  argue  that  they  do  not  need  to  spray,  because  in  the 
locality  in  which  they  live  late  blight  La  rarely  destructive. 
An  experiment  bearing  on  this  phase  of  the  subject  was  made 
by  the  New  York  Experiment  Station  on  Long  Island  in 
1896.38  Eight  and  one-half  acres  of  potatoes  were  sprayed 
live  times  with  Bordeaux.  Paris  green  being  added  in  the  first 
three  sprayings.  The  sprayer  used  was  a  one-horse,  two- 
wheeled  affair  operated  by  one  man.  who  pumped  and  drove, 
spraying  -t  rows  at  a  time.  There  were  4  varieties:  White 
Elephant,  Green  Mountain  (late).  Defender  (medium),  and 
Victor  Rose  (early).  A  few  rows  of  each  variety  were  left 
unsprayed.  In  the  fall  the  yield  of  the  unsprayed  rows  of 
each  variety  was  compared  with  the  same  number  of  adjacent 


15 

sprayed  rows  of  the  same  variety.     Spraying  increased  the 
yield  as  follows: 

Bushels 
per  acre. 

On  White  Elephant 60 

On  Green  Mountain 62 

On  Defender 16 

On  Victor  Rose 5 


View. 


45 


There  was  no  trace  of  late  blight  on  the  unsprayed  rows. 
The  increased  yield  on  the  sprayed  rows  was  due  to  the  pre- 
vention of  early  blight,  stimulation  of  the  plants,  and  better 
control  of  flea-beetles  and  Colorado  beetles.  The  average  per- 
son would  have  said  that  the  unsprayed  rows  did  not  suffer 
enough  from  blight  and  insects  to  materially  affect  the  yield. 
Nevertheless  spraying  gave  good  results  on  the  two  late  vari- 
eties. On  the  early  varieties  the  gain  was  small.  It  is  doubtful 
if,  under  such  circumstances,  it  pays  to  spray  early  potatoes. 

The  total  expense  of  the  five  sprayings  was  $4  per  acre. 
The  market  price  of  potatoes  being  25  cents  per  bushel,  the 
net  profit  in  spraying  the  two  late  varieties  was  $11  per  acre, 
and  this  in  a  season  when  there  was  no  late  blight  and  pota- 
toes were  cheap. 

In  some  seasons  spraying  will  pay  well.  In  others  there 
may  be  a  loss.  As  the  work  must  be  commenced  before  it  is 
known  whether  blight  will  appear,39  the  important  thing  to 
know  is  whether  it  pays  on  the  average.  There  is  little  doubt 
that  in  the  northeastern  United  States  it  will  pay  well  one 
year  with  another,  if  properly  managed;  but  from  Ohio  west 
this  remains  yet  to  be  determined  by  experiment.  Every 
potato  grower  who  is  in  doubt  should  give  spraying  a  thorough 
trial,  always  leaving  some  unsprayed  rows  for  comparison.*0 
We  incline  to  the  opinion  that  potato  spra}Ting  will  be  found 
profitable  over  all  that  portion  of  the  United  States  lying 
east  of  the  Mississippi  and  north  of  the  Ohio  River.  The 
benefits  of  spraying  to  the  potato  crop  are  greatly  underesti-  ^" 
mated  by  farmers. 

A  good  job  of  spraying  can  be  done  at  a  total  expense  of 
$4  to  $6  per  acre  for  five  applications. 

Philosophy  of  Spkaying. — Spra}Ting  is  preventive  not 
curative.  Once  within  the  tissue  of  the  leaf  the  blight  fungus 
is  bevond  control.  To  be  effective  the  spray  must  be  applied 
before  the  fungus  spores  have  germinated.  The  leaves  should 
be  coated  with  Bordeaux  mixture,  so  that  any  spores  falling 


16 

Vieic 

upon  them  will  be  unable  to  germinate.  If  the  disease  is  thus 
prevented  from  establishing  itself  upon  the  Leaves  there  i-  do 
chance  for  the  formation  of  spore-  to  fall  upon  the  ground 
and  cause  rot  of  the  tubers.  It  is  unsafe  to  postpone  spray- 
ing until  the  appearance  of  the  blight,  for  the  reason  that  it 
i-  usually  not  observed  until  after  it  has  become  well  estab- 
lished and  the  spore-  scattered  broadcast 

Bordeaux  v.  Patented  Fungicides. — There  are  upon  the 
market  numerous  patented  fungicides  which  are  offered  as 
substitutes  for  Bordeaux  mixture.  It  is  not  profitable  to  use 
them.  They  are  less  efficient  and  more  expensive.  For  pot  a 
toes,  at  least,  there  is  nothing  at  present  known  which  is 
superior  to  the  home-made  liquid  Bordeaux  mixture  prepared 
from  lime  and  blue  vitriol.  Soda  Bordeaux  is  not  recom- 
mended; neither  is  dry  Bordeaux  mixture,  except  where  the 
liquid  form  can  not  well  be  used. 

TREATMENT   FOR   SCAB. 

47  Scab  can  not  be  prevented  by  spraying  the  tops.     When 

soil  once  becomes  thoroughly  impregnated  with  the  scab  fun- 
gus it  is  impossible  to  grow  potatoes  fit  for  market,  and  there 
is  nothing  to  be  done  except  to  plant  to  some  other  crop  than 
potatoes  for  a  few  years.  How  long  the  scab  fungus  can  live 
in  the  soil  is  not  known,  but  it  must  be  several  years.  How- 
ever, much  of  the  disease  may  be  worked  out  of  the  soil  in 
the  same  way  that  land  may  be  cleared  of  weeds,  by  cultiva- 
tion, when  none  are  permitted  to  go  to  seed.  During  this 
process  beets  should  not  be  planted  on  the  land,  for  they  har- 
bor the  fungus.  Neither  should  lime,  wood  ashes,  or  stable 
manure  be  used,  for  these  substances  make  the  soil  alkaline 
and  favorable  to  the  growth  of  the  fungus.41  By  some  it  is 
believed  that  the  plowing  under  of  green  crops,  especiallv 
rye,  is  of  advantage,  because  it  tends  to  make  the  soil  acicL" 
Doctor  Halsted.43  of  the  New  Jersey  Station,  has  recom- 
mended flowers  of  sulphur  applied  in  the  open  furrows  at 
planting  time  at  the  rate  of  300  pounds  per  acre.  In  some 
soils  the  sulphur  treatment  ma}T  be  beneficial,  but  usually  it 
helps  but  little  and  can  not  be  recommended. 

The  most  satisfactory  method  of  combating  scab  is  to  care- 
fully guard  against  its  introduction.  As  the  chief  mode  of 
disl  ribution  is  by  means  of  diseased  seed  tubers,  all  seed  should 
be  disinfected  before  planting.  This  is  best  accomplished  by 
soaking  the  seed  tubers  for  two  hours  in  a  solution  of  formalin. 
1  pint  to  30  gallons  of  water.44     The  tubers  are  then  spread 


17 

out  to  dry  and  afterwards  cut  and  planted  in  the  usual  manner. 
Crates  or  sacks  used  for  holding  the  treated  tubers  should, 
likewise,  be  disinfected.  The  disinfection  may  be  done  at  any 
convenient  time,  preferably  a  few  days  before  planting.  The 
same  solution  may  be  used  several  times.  This  treatment 
kills  the  scab  germs  without  injuring  the  germination  of  the 
tubers.  If  treated  tubers  are  planted  in  a  scab-free  soil  a 
clean  crop  may  be  confidently  expected;  but,  if  planted  in  soil 
already  infested  by  the  fungus,  treatment  avails  but  little. 

An  older  and  probabl}T  better  known  method  of  disinfection 
is  by  the  use  of  corrosive  sublimate  as  follows:45  Dissolve  2 
ounces  of  corrosive  sublimate  in  2  gallons  of  hot  water  in  a 
wooden  or  earthen  vessel;  when  dissolved  add  enough  water 
to  make  14  gallons.  Soak  the  tubers  in  this  solution  one  and 
one-half  hours. 

The  two  methods  are  equally  effective,  but  the  former  is  to 
be  preferred  because  the  solution  is  easier  to  prepare,  is  not 
poisonous,  and  does  not  corrode  metals. 

It  should  be  borne  in  mind  that  land  may  become  infected 
by  the  washings  from  scab-infested  fields,  by  the  use  of  manure 
from  animals  fed  on  uncooked,  scabby  potatoes  or  beets,  and 
by  means  of  implements  used  in  cultivation. 

The  disinfection  treatment  for  scab  will  also  kill  any  Rhi- 
zoctonia  which  may  be  on  the  tubers,  but  no  method  is  known 
of  ridding  the  soil  of  Rhizoctonia. 

TREATMENT  FOR  BACTERIAL  WILT  AND  DRY  ROT. 

For  these  two  diseases  no  practical  remedy  is  known. 
Spraying  does  but  little  if  any  good,  because  most  of  the 
trouble  is  below  ground.  On  badly  infested  land  potato  cul- 
ture should  be  abandoned  for  several  years.  Tubers  from 
diseased  fields  should  not  be  used  for  seed. 

Since  bacterial  wilt  attacks  also  the  eggplant  and  tomato, 
these  plants  should  not  be  grown  on  land  where  potatoes  have 
been  affected  or  vice  versa. 


View. 


APPENDIX. 


LANTERN    SLIDES. 


No.  of 
view. 


1.  Early  stage  of  early  blight. 

From  Vermont  Sta.  Bui.  72,  fig.  9. 

2.  Advanced  stage  of  early  blight. 

From  U.  S.  Dept.  Agr.,  Farmers'  Bui.  15. 

3.  Fungus  of  early  blight. 

1.  Single  spore  of  Alternaria  solani,  showing  germ  tubes  from  three  cells. 

2.  Two  spores  of  Alternaria  solani,  germinating  and  penetrating  surface  of  living  potato  leaf; 

b,  b,  through  stomates;  c,  through  epidermis. 

3.  Spores  of  Alternaria  solani,  showing  peculiar  forms. 

4.  Spores  of  saprophytic  Alternaria  fasciculata  occurring  on  potato  leaves,  three  mature  and 

three  immature;  central  one  germinating. 

5.  Fruiting  branch  of  Alternaria  fasciculata. 
From  Vermont  Sta.  Bui.  72,  fig.  11. 

4.  Tip  burn. 

From  Vermont  Sta.  Bui.  72,  fig.  6. 

5 .  Late  blight.     Frost-like  mildew  on  under  surface  of  leaf. 

Dead  brown  spots  surrounded  on  the  under  surface  by  a  ring  of  frost-like  mildew  whith  is 
composed  of  the  spore  stalks  and  spores  of  the  fungus. 
From  New  York  State  Sta.  Bui.  241,  PL  XL 

6.  Advanced  stage  of  late  blight. 

Lower  leaves  all  dead  and  black;  only  few  green  leaves  at  the  top. 

From  New  York  State  Sta.  Bui.  241,  PI.  X. 

7.  Fungus  of  late  blight. 

1.  Section  through  a  diseased  leaf,  showing  the  mycelium  in  the  tissues  and  two  external 

spore  stalks  projecting  through  a  stoma. 

2.  Spores  and  spore  stalks  more  enlarged. 

3.  Series  of  drawings  showing  successive  stages  in  the  development  of  a  spore. 

4.  Feeding  threads  (hyphae)  running  between  the  cells  of  a  potato  tuber. 

5.  Seriesof  figures  showing  the  germination  of  a  spore:  a,  mature  spore;  d,  zoospores  escaping; 

h,  zoospore  beginning  to  germinate;  i,j,  k,  successive  stages  in  growth  of  germ  tube;  I, 
entrance  of  germ  tube  into  leaf  through  a  stoma. 

6.  Section  of  leaf  showing  the  penetration  of  a  germ  tube  into  the  epidermis  through 

the  cell  wall. 

From  U.  S.  Dept.  Agr.  Rpt.  for  1888,  PI.  II. 

8.  Rot  of  tubers  following  late  blight. 

Slightly  affected  tubers  shown  in  cross  section. 

From  New  York  Cornell  Sta.  Bui.  113,  fig.  98. 

9.  Bacterial  wilt.     Healthy  and  inoculated  plants. 

Plant  on  left  inoculated  by  placing  on  it  a  handful  of  Colorado  potato  beetles  which  had 
fed  for  some  hours  on  diseased  vines.  The  beetles  were  left  on  over  night  and  gnawed  the 
plant  in  many  places,  but  did  not  injure  it.    There  were  no  symptoms  of  disease  until  after 

(19) 


20 


IT,  but  after  that  rapid 
graphed  three  weeki  after  looealatli  a.    At  thi>  ti  -tagesof 

I   OH    light   is  u   heeJthj   plant   from  the  -an  •  as  that  the 

-;  riu'l  bj  ::• 

From  U.  8.  Dept  Agr.,  1  >i\ .  Veg.  Phya  and  I'aih.  Bui.  12  md  4. 

lO.      Hill  <•:  potatoes  partly  diseased  with  dry  rot 

From  U.  s.  Dept  Agr.,  Bureau  ol  Plant  [ndoatry  Bol  56,  Erontiepii 
i  l .     Bundle  blackening  at  stem  end  <>f  tutors. 

Tub  with  dry-rot  fangOS,  Fusarium  oxysporum,  cut  across  at  steal  and  to  show 

the  black  or  brown  streaks.    Outwardly  these  tubers  appeared  sound. 

Prom  U.  S.  Dept  Alt.,  Bureau  of  Plant  Industry  Bol  66,  PL  IV. 
i2.    Tubem  affected  with  dry  end  rot 

Late  stage  of  the  lllnrasn  in  stored  tubers  exposed  to  warm  dry  air. 

From  U.  S.  Dept.  Alt..  Bureau  <>f  Plant  Industry  Bui.  55,  PI.  VI. 

13.  Pongee  of  dry  rot. 

Shows  mycelium,  spores,  and  germ  tubes  of  the  potato  dry-rot  fungus.  Fusarium,  oxysporum. 
From  U.  S.  Dept.  Agr.,  Bureau  of  Plant  Industry  Bui.  55,  PI.  VIII. 

14.  Tubers  affected  with  scab. 

From  New  York  Cornell  Sta.  Bul.  163,  fig.  63. 

15.  Scab  induced  by  artificial  inoculation. 

From  Connecticut  State  Sta.  Rpt.  1890,  PI.  I. 

16.  Sugar  beets  affected  with  scab. 

From  New  York  Cornell  Sta.  Bul.  163,  cover  illustration. 

17.  Rosette  of  the  potato  plant. 

18.  Rhizoctonia  sclerotiaon  potato  tubers. 

From  New  York  Cornell  Sta.  Bul.  186,  cover  illustration. 

19.  Hyphae  of  beet  Rhizoctonia. 

Although  the  beet  Rhizoctonia  is  different  from  the  potato  Rhizoctonia  the  feeding 
threads  (hyphae)  of  the  two  speeies  look  so  nearly  alike  as  to  be  indistinguishable  from 
them.    Hence,  we  may  use  the  beet  Rhizoctonia  to  illustrate  the  potato  Rhizoctonia. 
From  New  York  Cornell  Sta.  Bul.  163,  fig.  51. 

20.  Colorado  potato  beetle. 

From  Smith's  "Economic  Entomology,"  fig.  206,  and  in  many  other  pub- 
lications on  insects. 

21.  Blister  beetles. 

Three  common  species  of  blister  beetles  infesting  potatoes:  a,  the  ash-gray  one  (Macrobasu 

unicolor);  b,  the  black  one  t  Epicautu  penntylraniai). 

From  Smith's  "Economic  Entomology,"  figs.  232  and  233. 

22.  The  flea-beetle  and  its  work. 

From  Vermont  Sta.  Bul.  72,  figs.  1  and  2. 

23.  Flea-beetle  injury  reduced  by  spraying. 

Shows  the  number  of  flea-beetle  punctures  found  in  50  leaflets  from  adjacent  rows  sprayed 
with  different  mixtOI 

From  Vermont  Sta.  Bul.  72,  figs.  1  and  2. 

24.  Damage  from  flea-beetlee  and  grasshoppere  reduced  by  spraying. 

The  nnsprayed  rows  at  the  right  wore  treated  with  Paris  green  sufficiently  to  prevent  the 
Colorado  potato  beetle  doing  damage,  but  the  flea-beetles  end  grasshoppers,  both  of  which 
were  numerous,  were  not  cheeked.  The  rows  at  the  left  were  sprayed  three  times  with 
Bordeaux. 

The  sprayed  rows  yielded  152  bushels  per  acre  and  unsprayed  118  bushels.  Most  of  this 
gain  was  due  to  the  action  oi  tht>  Bordeaux  as  a  deterrent  to  flea-beetles  and  grasshoppers. 
Photograph  taken  AJBgOSt  81,  l^'.M. 

From  Vermont  Sta.  Bul.  44.  fig.  14. 


21 

No.  of 
view. 

25.  Single  unsprayed  hill  from  field  shown  in  \<>.  24. 

The  upper  leaves  cut  otT  by  gi&nhoppen. 

From  Vermont  Sta.  But  44,  fig.  13. 

26.  Single  sprayed  hill  from  field  shown  in  No.  24. 

From  Vermont  Sta.  Bui.  44,  fig.  12. 

27.  Correct  method  of  preparing  Bordeaux  mixture. 

The  vitriol  water  and  the  limewater  should  both  be  diluted  before  mixing. 

28.  Bordeaux  mixture  made  in  different  ways. 

Glass  cylinders  showing  relative  rapidity  of  settling  of  the  precipitate  in  Bordeaux  mixture 
made  in  different  ways.  Each  cylinder  stood  one  hour  after  making  before  being  photo- 
graphed. 

1.  Made  by  pouring  dilute  lime  into  dilute  sulphate  slowly. 

2.  Made  by  pouring  dilute  sulphate  into  dilute  lime  slowly. 

3.  Made  properly  (as  5),  but  using  hot  lime  milk. 

4.  Mixture  made  as  in  5,  but  less  thoroughly  stirred. 

5.  Properly  made  Bordeaux  mixture,  i.  e.,  from  cold,  dilute  solutions,  quickly  united  and 

thoroughly  stirred. 

6.  Made  same  as  5,  but  using  concentrated  solutions. 

7.  Properly  made  mixture  one  day  old. 

8.  Old  Bordeaux  mixture  made  two  weeks  before. 

9.  "Bordeaux  powder"  mixed  with  water. 
From  Vermont  Sta.  Bui.  72,  fig.  13. 

29.  Good  facilities  for  making  Bordeaux  mixture. 

The  property  of  W.  H.  Satterly,  Mattituck,  Long  Island,  X.  Y.,  who  uses  it  for  the  prepa- 
ration of  Bordeaux  for  spraying  potatoes.  The  barrel  with  a  shovel  in  it  contains  the  stock 
lime.  The  other  barrel,  standing  against  the  building,  contains  a  stock  solution  of  copper 
sulphate.  The  two  barrels  in  front  on  the  upper  platform  are  "  dilution  "  barrels,  one  for 
lime  water,  the  other  for  copper-sulphate  solution.  The  two  barrels  on  the  lower  platform 
are  "mixing "  barrels.  By  means  of  two  short  pieces  of  hose  the  contents  of  the  two  dilu- 
tion barrels  are  drawn  off  simultaneously  into  one  of  the  mixing  barrels.  From  the  mixing 
barrel  the  prepared  mixture  runs  into  the  spray  tank  through  another  short  piece  of  hose. 
The  water  required  comes  from  a  tank  in  the  barn,  which  is  filled  by  means  of  a  windmill. 
There  is  no  dipping  and  lifting  of  water  or  Bordeaux.    The  work  is  all  done  by  gravity. 

30.  Compressed-air  sprayer  for  use  in  gardens. 

The  multispray  compressed-air  sprayer.  Capacity  of  tank,  5  gallons,  but  only  about  3 
gallons  of  liquid  can  be  used  at  one  time.  Remainder  of  space  is  required  for  compressed 
air.    Price,  $5. 

31.  Knapsack  sprayer. 

Knapsack  sprayer.    Price,  $15.    Capacity  of  tank,  5  gallons. 

32.  Barrel  spray  pumps. 

Two  good  barrel  spray  pumps.    Price,  815  each. 

33.  One  method  of  using  a  barrel  outfit. 

From  Vermont  Sta.  Bui.  72,  fig.  16. 

34.  An  excellent  potato-spraying  outfit. 

A  pump  in  a  100-gallon  tank.  Sprays  five  rows  at  a  time  with  two  Vermorel  nozzles  per 
row.  One  man  pumps  and  drives  at  the  same  time.  Drawn  by  one  horse.  For  use  on 
hilly  land  a  50-gallon  tank  would  be  better. 

From  New  York  State  Sta.  Bui.  241,  PI.  V. 

35.  A  power  sprayer  for  potatoes. 

Potato  sprayer.  Price.  S75.  Sprays  five  rows  at  a  time  with  one  nozzel  per  tow.  Same 
sprayer  shown  in  Xo.  41. 

36.  Vermorel  nozzles. 

37.  Late  blight  prevented  by  spraying. 

Rows  at  left  sprayed  three  times  with  Bordeaux.  Photograph  made  Sept.  10.  The  sprayed 
rows  yielded  at  the  rate  of  324  bushels  per  acre,  while  the  unsprayed  rows  yielded  only  100 
bushels  per  acre, 

From  Vermont  Sta.  Bui.  40,  fig.  6. 

38.  Total  yield  of  marketable  tubers  from  two  sprayed  rows  in  field  shown  in  No.  37. 


29 

No.  of 

view. 

'.I'.K     Total  yield  of  marketable  toben  from  two  unsprayed  rows  in  field  shown  in 
No. 

4(>.      Tot. it«.  BfHS]  tag  experiment  at  the  rk  Experiment  Station. 

Th.  k-  was  spra\v<l  live  times  in  all.     Yield  lisj 

acre.     The  am  iptayed  three  :  !  :>'h»  l.usl.'  The  unsprayed  row 

yielded  l'U  hush>  i-  pes  am-.  These  rows  were  Nor.  8,  9,  and  10  in  the  ten  year  experiment 
■J  Genera  in  1901  There  was  hut  little  rot.  The  increased  yield  on  sprayed  row-  na-  due 
chiefly  to  prolonged  growth  <>f  the  plant-. 

From  New  York  State  Sta.  Bui.  264,  PI.  III. 

4  1 .     Bpraying  in  the  Salisbury  experiment. 

Another  view  oJ  the  sprayer  shown  in  No.  35. 
From  New  York  State  Sta.  Kill.  241,  PI.  VI. 

4"J.     Facilities  for  making  Bordeaux  in  Salisbury  experiment. 

A  spring  supplies  the  water  which  is  piped  into  the  larire  tank  at  the  left. 

4.'$.     Sprayed  and  unsprayed  rows  in  Salisbury  experiment 
Photograph  taken  Oct.  3,  1903. 
From  New  York  State  Sta.  Bui.  241,  PL  VII. 

44.  Results  in  the  Salisbury  experiment. 

4  5.  Results  of  spraying  when  there  was  no  late  blight. 

46.  What  spraying  does. 

4  7.  Treatment  for  stab. 


DIRECTIONS    FOR    SPRAYING. 

I. — Copper  Sulphate  and  Copperas. 

Many  persons  confuse  copper  sulphate  with  copperas.  Copper  sulphate  is  blue 
vitriol,  also  called  blue  stone.  It  contains  copper  and  is  used  in  the  preparation  of 
Bordeaux  mixture. 

Copperas  is  an  entirely  different  thing.  It  is  iron  sulphate.  It  does  not  contain 
copper  and  can  not  be  used  for  making  Bordeaux. 

The  crystals  of  the  two  substances  are  somewhat  similar  in  appearance,  but  may 
be  readily  distinguished  by  their  color.  Copper  sulphate  crystals  are  blue,  while 
those  of  copperas  are  greenish. 

II. — Bordeaux  Mixture. 

The  following  discussion  of  Bordeaux  mixture  is  taken  from  Bulletin  No.  243  of 
the  New  York  State  Experiment  Station: 

"  The  essential  ingredients  for  making  Bordeaux  mixture  are  freshly  slaked  lime  and 
copper-sulphate  solution.     The  fungicidal  value  lies  in  the  copper. 

"  The  lime  is  added  only  to  prevent  injury  to  foliage  and  to  make  the  mixture 
more  adhesive  and  more  easily  seen  after  being  applied  to  the  foliage.  Limewater 
will  not  do.  A  very  thin  white  wash  made  from  lime  and  water,  commonly  called 
milk  of  lime,  is  needed.  The  relative  amounts  of  lime  and  copper  sulphate  which 
are  used  may  be  greatly  varied,  because  a  great  excess  of  lime  may  be  used  without 
injury  to  foliage,  but  it  is  absolutely  essential  that  enough  lime  be  used,  or  injury  to 
foliage  will  surely  follow.  It  is  not  safe  to  use  less  than  two-thirds  as  much  lime 
by  weight  as  of  the  undissolved  copper  sulphate;  that  is  to  say,  in  the  proportion  of 
2  pounds  of  lime  to  3  pounds  of  copper  sulphate.     *    *    * 

"  Importance  of  good  lime,  properly  slaked. — Prof.  L.  R.  Jones  and  Mr.  W.  A.  Orton, 
of  the  Vermont  Experiment  Station,  make  the  following  comments  on  the  impor- 
tance of  good  lime,  properly  slaked:  'The  quality  of  the  lime  and  the  method  of 
slaking  it  have  much  influence  upon  the  mixture.  Thus,  other  conditions  being 
equal,  a  mixture  made  from  a  poorly  slaked  lime  settled  19  per  cent  (of  the  height 
of  a  column  in  a  glass  cylinder)  in  an  hour,  while  a  mixture  made  from  properly 
slaked  lime  settled  only  8  per  cent  in  the  same  time.  Lime  that  had  been  partially 
air  slaked  gave  still  poorer  results.  The  lime  should  be  fresh,  clean,  and  firm.  In 
slaking,  the  best  results  were  obtained  by  adding  at  first  only  a  small  amount  of 
water,  preferably  hot,  and  then,  as  slaking  begins,  adding  cold  water  in  small 
amounts  as  needed,  never  adding  much  at  a  time  and  never  allowing  the  lime  to 
become  dry.  When  too  much  water  is  added  small  lumps  of  lime  are  apt  to  be  cov- 
ered and  remain  unslaked.  When  the  lime  is  fully  slaked  it  should  be  fully  diluted 
by  adding  water  slowly  while  stirring.' 

"Strength  of  Bordeaux  mixture. — The  strength  of  the  Bordeaux  mixture  may  be 
wisely  varied  under  different  conditions.  For  ordinary  use  in  apple  orchards  where 
a  good  spray  is  thoroughly  applied  a  strength  of  from  1-to-ll  or  l-to-10  will  usually 
be  satisfactory;  for  treating  the  potato  a  strength  of  from  l-to-8  or  l-to-7  may  well 
be  used.     For  the  very  tender  foliage  of  Japan  plums  and  of  peaches  the  mixture,  if 

(23) 


24 

used  at  all.  may  be  reduced  to  the  l-to-25  formula.     The  designations  used  for  the 
various  formate  are  easily  understood.     For  example,  the  1-to-ll  mixtore  ii  made 
by  osing  l  pound  of  copper  sulphate  for  making'  11  gallons  of  Bordeaux  mixture. 
"  \£ethod  of  preparation  of  Bordeaux  mixture. — It  will  be  seen  later  that  lime  may 

be  -laked  and  thus  k«-pt  in  stock  and  that  a  stork  solution  of  «••  »]>j>«*r  sulphate  may 
d;  hut  in  order  to  gel  a  clear  understanding  of  the  subject  the  simple  method 

of  weighing  ami  mixing  tin-  ingredients  will  lir-t  be  presented. 

Bordeaux  mixture,  l  t>>  10  formula. 
(To  make  .~>n  gsll<  H 
Copper  -ulj .hate  I  blue  vitriol) pound.-. . 

Quicklime  <  not  slaked ) do 3J-5 

Water gallon! 

"Stock-Inn,  paste. — Several  ways  are  known  whereby  the  Bordeaux  mixtore  may 
be  tested  to  find  out  whether  enough  lime  has  been  added  to  unite  with  all  of  the 
copper  sulphate,  thus  avoiding  the  necessity  for  weighing  the  lime.  This  permits  of 
the  slaking  of  considerable  quantities  of  lime  at  onetime.  The  lime  may  then  he 
kept  in  excellent  condition  for  some  time  if  covered  with  water  to  exclude  the  air. 

"  /',  rrocjfOtdd  of  potassium  test — The  test  most  commonly  used  for  determining 
whether  or  not  enough  lime  has  been  put  into  the  Bordeaux  mixture  to  combine 
with  all  of  the  copper  sulphate  is  the  ferrocyanid  of  potassium  test,  commonly  called 
the  'ferrocyanid'  test. 

"Potassium  ferrocyanid  is  also  called  yellow  prussiate  of  potash.  It  is  a  very 
poisonous  yellow  salt  which  dissolves  readily  in  water.  A  few  cents'  worth  dissolved 
in  about  ten  times  its  bulk  of  water  will  ordinarily  last  through  the  season.  In  using 
this  test  fill  the  spray  tank  half  to  two-thirds  full  of  the  copper-sulphate  solution; 
then  pour  in  the  milk  of  lime.  Stir  the  mixture  thoroughly  and  add  a  drop  of  the 
potassium  ferrocyanid.  If  enough  lime  has  been  added,  the  drop  will  not  change 
color  when  it  strikes  the  mixture;  otherwise  it  will  immediately  change  to  a  dark 
reddish-brown  color.  More  lime  must  then  be  added  until  the  ferrocyanid  does 
not  produce  the  reddish-brown  color.  Even  after  the  test  shows  no  color  more  lime 
should  be  added,  so  as  to  be  sure  that  all  of  the  copper  is  precipitated;  for  in  ca«e  the 
mixture  has  not  been  thoroughly  stirred  some  of  the  copper  may  still  remain  in 
solution  in  the  bottom  of  the  barrel  while  the  test  shows  no  color  at  the  surface. 

"If  the  formula  calls  for  a  quantity  of  lime  equal  to  the  copper  sulphate  in  weight, 
a  half  more  lime  than  is  required  to  satisfy  the  ferrocyanid  test  should  be  added  to 
the  mixture.  Suppose,  for  example,  one  wished  to  take  6  pounds  of  copper  sulphate 
and  6  pounds  of  lime  with  60  gallons  of  water  to  make  60  gallons  of  Bordeaux  mix- 
ture and  to  use  the  ferrocyanid  test.  When  the  test  first  shows  that  enough  lime  is 
present  to  combine  with  all  of  the  copper  sulphate  the  mixture  will  contain  somewhat 
less  than  4  pounds  of  lime.  To  complete  the  mixture  according  to  the  6-0-60 
formula  requires  the  addition  of  half  as  much  lime  as  has  already  been  used;  that  is 
to  say,  it  requires  2  pounds  more  of  lime,  or  the  equivalent  amount  of  thelime  paste. 

"Mixing  tanks. — It  is  convenient  to  have  special  tanks  for  mixing  the  Bordeaux. 
Thus  the  tank  for  the  lime  may  be  placed  so  that  its  contents  may  be  drawn  off  into 
the  tank  in  which  the  copper-sulphate  solution  is  put  and  in  which  the  mixture  is 
made.  Tin-:  tank  may  likewise  be  elevated  so  that  the  prepared  Bordeaux  mixture 
may  be  drawn  off  into  the  spray  tank.  By  this  arrangement  it  is  possible  to  avoid 
the  necessity  of  dipping  and  lifting  the  mixture.  If  these  tanks  are  so  located  with 
relation  to  the  water  supply  that  the  water  may  be  run  into  the  lime  tank,  it  i> 
ble  to  avoid  the  necessity  of  dipping  and  lifting  every  gallon  of  mixture  thai 
into  the  spray  tank.  The  lime  may  also  be  Btrainedboth  when  it  is  put  into  thelime 
md  when  it  is  run  from  there  into  the  Bordeaux  vat,  which  is  an  advantage." 


25 

III. — Arsenite  of  Soda    (Kedzie  Formula). 

White  arsenic pounds. .       2 

Sal  soda do 8 

Water gallons. .       2 


Boil  until  the  arsenic  is  all  dissolved,  which  will  take  about  fifteen  minutes. 
Replace  the  water  lost  in  boiling,  as  otherwise  some  of  the  material  will  crystallize 
upon  cooling.  This  makes  a  stock  solution  of  arsenite  of  soda,  which  may  be  placed 
in  tightly  stoppered  jugs  or  bottles  and  kept  on  hand  for  use  as  needed.  The  vessels 
used  in  making  and  storing  the  solution  should  be  plainly  labeled  "Poison"  and 
never  used  for  any  other  purpose. 

Two  quarts  of  this  stock  solution  are  equivalent  to  1  pound  of  Paris  green  and  is 
the  quantity  which  should  be  used  on  an  acre  of  potatoes.  At  the  rate  of  1  to  2 
quarts  in  50  gallons  it  may  be  used  with  Bordeaux  mixture  without  danger  of  injury 
to  the  foliage,  but  it  must  not  be  used  alone.  Even  with  lime  water  it  can  not  be 
safely  used  at  a  greater  strength  than  1  quart  of  stock  solution  with  4  pounds  of  lime 
in  50  gallons  of  water. 

IV. — Concerning  the  Number  of  Sprayings. 

There  is  great  diversity  of  opinion  as  to  the  number  of  sprayings  which  is  most 
profitable.  Some  hold  that  two  or  three  sprayings  are  sufficient.  Others  would 
spray  frequently  throughout  the  whole  season. 

Conditions  vary  so  much  that  no  invariable  rule  can  be  made.  The  farmer  must 
rely  chiefly  on  his  own  judgment.  Probably  the  rule  which  most  nearly  fits  all 
cases,  and  the  one  to  be  followed  when  in  doubt,  is  the  following:  Commence  spray- 
ing when  the  plants  are  6  to  8  inches  high  and  repeat  the  treatment  regularly  at 
intervals  of  ten  to  fourteen  days  as  long  as  the  plants  live. 

Usually  "bugs"  must  be  treated  when  the  plants  are  a  few  inches  high.  Often 
flea-beetles  are  prevalent  at  the  same  time.  By  using  Bordeaux  and  poison  together 
both  these  insects  may  be  more  effectively  fought  than  by  using  poison  alone.  In 
another  two  weeks  the  second  brood  of  bugs  has  appeared.  A  second  spraying  must 
be  made  for  these.  In  two  weeks  more  the  plants  are  in  bloom  and  quite  large. 
They  must  now  be  sprayed  for  blight,  and  it  is  not  easy  to  reach  the  lower  leaves. 
Unless  the  two  early  sprayings  have  been  made,  it  is  difficult  to  protect  the  lower 
leaves  and  they  fall  a  prey  to  both  early  and  late  blight.  Where  the  vines  grow 
large  this  is  an  important  matter. 

Another  advantage  in  commencing  early  is  that  the  plants  are  always  protected 
against  an  outbreak  of  late  blight.  As  a  rule  it  is  unsafe  to  postpone  spraying  until 
the  appearance  of  blight.  Usually  the  blight  becomes  thoroughly  established  in  a 
field  before  it  is  observed.  In  any  case  it  is  necessary  to  act  very  promptly,  and 
there  are  likely  to  be  unforeseen  hindrances,  such  as  lack  of  materials  or  the  sprayer 
being  out  of  order.  Then,  too,  it  often  happens  that  the  outbreak  of  blight  occurs 
during  a  period  of  wet  weather  when  it  is  almost  impossible  to  get  into  the  field  to 
spray.  The  only  sure  way  to  avoid  such  difficulty  is  to  commence  early  and  spray 
regularly  at  intervals  of  10  to  14  days,  as  above  directed.  One  of  the  chief  causes  of 
failure  is  beginning  too  late. 

The  frequency  of  the  spraying  should  depend  somewhat  upon  the  thoroughness 
with  which  the  work  is  done.  In  giving  the  above  directions  for  spraying  it  is 
assumed  that  the  quantity  of  Bordeaux  applied  at  each  spraying  is  at  least  40  gallons 
per  acre.  If  using  a  sprayer  which  applies  but  25  gallons  per  acre,  once  in  two 
weeks  is  not  often  enough.  In  such  cases  an  application  should  be  made  every  week. 
When  the  vines  are  large  and  the  weather  favorable  to  late  blight  at  least  100  gallons 
per  acre  are  required  to  do  good  work.  The  general  tendency  of  farmers  is  to  make 
too  light  applications.     Many  fail  because  they  are  too  saving  of  time  and  maternal. 


26 

v      Spb  \»  iv.'.   Before  Rain. 

Borne  hesitate  to  spray  potatoes  when  it  looks  like  rain.  They  argue  that  the  rain 
will  trash  <>ff  the  Bordeaux  and  Decessitate  the  work  being  done  over.  Lei  us  inquire 
into  this  matter.  It  la  in  rainy  weather  thai  spraying  it  most  needed,  because  it  is 
then  that  the  late  blight  spread*  mosl  rapidly.  The  beating o!  the  rain  scatter-  the 
Bporefl  <>t"  the  blighl  fungus  ami,  the  conditions  for  their  germination  being  excellent, 

infection  occur-  readily.  Mosl  of  the  infection  takes  place  during  rainy  weather. 
In  dry  weather  the  disease  makes  slow  progress  because  the  Bporefl  mii-t  have  mois- 
ture in  which  to  germinate.     Moreover,  much  drying  kills  the  Bporefl  outright 

Because  of  these  facts  the  besl  time  to  spray  is  shortly  before  rain.  If  there  ii 
Bufficienl  time  for  the  Bordeaux  to  gel  thoroughly  dry  on  the  Leaves  before  the  rain 

comes,  it  is  all  right  The  leaves  are  them  protected.  Spores  falling  on  them  will 
he  unable  to  germinate.  Even  when  the  mixture  does  not  get  dry  spraying  must  do 
some  good;  hut  in  such  cases  another  spraying  should  he  made  as  soon  as  possible. 
Never  Btop  spraying  because  rain  threatens.  On  the  contrary,  make  a  special  effort 
to  get  the  Bpraying  done  before  it  rains. 

VI. — Results  of  Spraying  Potatoes  in  Vermont. 


Variety. 


White  Star 

Do 

Do 

Do 

Do 

Polaris 

Do 

White  Star 

Average  3  varieties. 
Delaware 

Do 

Do 

Green  Mountain 

Delaware 

Do 


Average  for  15  years. 


Planted. 


May 

May 

May 
Apr. 
May 
May 
June 
May 
May 
May 
May 
Mav 
May 
May 
May 


11,1891 

20. 1892 

20. 1893 

26. 1894 

20. 1895 

15. 1896 
1,1897 

10. 1898 

18. 1899 
23,1900 

25. 1901 

15. 1902 
1,1903 

25,1904 
15, 1905 


Sprayed. 


Aug.  26,  Sept.  8 

July  30,  Aug.  13,25 

Aug.  1,16,29 

June  16,  July  17,  Aug.3( 

July  25,  Aug.  13, 31 

Aug.  7, 21 

July  27,  Aug.  17, 28 

July  21,  Aug.  10 

Julv  26,  Aug.  17,  Sept.  8. 

Aug.  4, 23 

Julv  20,  Aug.  21 

Aug.  1,20 

Aug.  10 

Aug.  1,  Sept.  1 

Aug.2,21 


Yield  per  acre. 


Where 
sprayed. 


Bushel*. 

313 

291 
338 
323 
389 
325 
151 
238 
229 
285 
170 
298 
361 
327 
382 


296 


Where 

not 
sprayed. 


Gain  per 
acre. 


Bushels. 


114 
251 

219 
257 
80 
112 
161 

54 

164 

237 
193 

221 


176 


BusheU. 

65 

192 

224 

72 

170 

68 

71 

126 

68 

60 

116 

134 

124 

134 

171 


119 


VII. — Benefits  of  Prolonged  Growth. 

Few  realize  how  great  a  difference  in  yield  results  from  prolonging  the  life  of  potato 
plants  two  or  three  weeks.  The  following  table,  showing  the  rate  of  development 
of  potato  tubers  at  different  stages  of  growth,  is  copied  from  Vermont  Station  Bulletin 
No.  72,  page  5: 

Yield  <>/  tuber*  at  different  dates,    White  Star  potatoes,  planted  May  SO. 


Date  of  digging. 


Total 

Yield  of 

yield  per 

market- 

acre. 

able  size. 

Busliels. 

Bushels. 

58 

30 

115 

75 

230 

163 

304 

234 

356 

303 

379 

353 

Average 
size  of 
tubers. 


August  2 

A.UgUlt  12 

AOgTlSt  22 

September  1  . 
September  12 
September  22 


Ounces. 
1.6 

2 

3.7 
1.  » 

5.7 


27 

VIII.— Making  Ex  pbbi  m  bnib. 

Farmers  do  not  experiment  as  much  as  they  should.  It  is  an  easy  matter  to  make 
potato-spraying  experiments  and  not  expensive.  Nevertheless  there  are  few  who 
attempt  anything  along  this  line  and  most  of  those  who  do  are  so  careless  in  their 
methods  that  they  are  unable  to  draw  trustworthy  conclusions  from  the  results  of 
their  experiments. 

A  fair  test  of  potato  spraying  requires  that  an  account  be  kept  of  the  expense,  care 
being  taken  to  avoid  unnecessary  expense.  Some  rows  should  be  left  unsprayed 
for  comparison,  and  these  unsprayed  rows  should  be  under  practically  the  same  con- 
ditions as  the  sprayed  rows.  They  must  be  of  the  same  variety,  on  the  same  kind  of 
soil,  treated  with  the  same  kind  and  quantity  of  fertilizer,  and  given  the  same  cultiva- 
tion. Finally,  the  experiment  rows  must  be  measured  with  a  tape,  not  paced;  and 
the  crop  on  them  must  be  weighed,  not  estimated. 

The  common  practice  of  judging  the  results  of  spraying  by  comparison  with  the 
unsprayed  fields  of  neighbors  is  to  be  condemned.  It  is  unreliable.  Again,  many 
persons,  after  having  begun  an  experiment  properly  by  leaving  a  few  unsprayed  rows, 
spoil  it  by  "guessing  at"  the  yield.  Had  they  completed  the  experiment  by  care- 
fully measuring  the  land  and  measuring  the  potatoes  on  the  sprayed  and  unsprayed 
rows,  they  would,  most  likely,  have  been  astonished.  A  difference  of  15  or  20 
bushels  per  acre  can  scarcely  be  detected  while  the  crop  is  growing,  or  even  after  the 
tubers  have  been  thrown  out  by  the  potato  digger;  and  yet  this  quantity  is  ordinarily 
sufficient  to  pay  the  expense  of  spraying.  For  a  noteworthy  example  of  the  impos- 
sibility of  correctly  estimating  differences  in  yield  by  the  eye,  see  New  York  State 
Station  Bulletin  No.  241,  page  263. 

IX. — Best  Time  to  Dig  Blighted  Potatoes. 

When  potatoes  are  attacked  by  late  blight  there  is  always  danger  that  the  tubers 
may  rot.  The  question  is  frequently  asked:  "Howr  soon  after  the  tops  begin  to 
blight  should  the  tubers  be  dug  in  order  to  avoid,  as  far  as  possible,  loss  from  rot?" 
This  subject  has  been  investigated  by  Professor  Jones,  at  the  Vermont  Experiment 
Station  (Seventeenth  Annual  Report,  pp.  391-395),  who  sums  up  the  results  of  his 
experiments  as  follows :  "When  potato  tops  have  been  killed  by  the  late  blight  fungus 
and  there  is  consequent  danger  of  rot  of  the  tubers,  do  not  dig  them  until  a  week  or  more 
after  the  tops  are  killed.  A  longer  delay  will  do  no  harm.  With  late  varieties, 
where  the  progress  of  the  disease  is  slow,  do  not  begin  digging  until  the  third  week 
of  September  at  the  earliest,  and  if  practicable  wait  until  after  the  tops  have  been 
killed  by  frost,"     (See  Vt.  Expt.  Sta.  Rpt.  18,  p.  279,  for  an  exception  to  this  rule.) 

Our  own  observations  lead  us  to  a  similar  conclusion.  If  the  tubers  are  to  be  stored 
they  should  not  be  dug  until  the  tops  are  dead  and  thoroughly  dry,  in  order  that  the 
fungus  spores  may  be  given  a  chance  to  dry  up  and  die.  As  long  as  the  tops  remain 
even  partially  green  the  spores  of  the  blight  fungus  continue  to  live.  In  the  process 
of  digging  the  tubers  become  covered  with  these  live  spores,  and  if  conditions  are  at 
all  favorable  more  or  less  rot  results.  This  explains  why  sprayed  potatoes  sometimes 
rot  more  in  storage  than  unsprayed  ones. 

In  this  connection  attention  should  be  called  to  the  objectionable  practice  of  cover- 
ing piles  of  tubers  with  potato  tops  to  protect  them  from  the  sun.  If  the  tops  have 
been  affected  with  late  blight  they  may  infect  the  tubers  and  cause  them  to  rot.  The 
danger  is  especially  great  if  the  tops  are  green  or  if  rain  comes  while  the  tubers  are 
thus  covered. 

X. — Is  it  Safe  to  Plant  Where  Potatoes  Blighted  the  Previous  Season? 

The  above  question  is  often  asked.  The  answer  depends  somewhat  upon  the  kind 
of  blight.     If  the  blight  in  question  is  late  blight  there  is  not  much  danger  of  the 


28 

being  carried  <»vcr  in  the  .-oil.      Bo  far  if   known  the  late  blight  doei  not  live 

over  winter  in  the  soil.     (For  a  diacnanon  of  this  nbject  see  Conn.  Kxpt.  Sta.  Rpt 
for  1906,  Tart  \',  I-]..  903-390.  i     However,  it  seems  probable  that  Bometimee  the  fangm 

may  be  carried  <>\er  in  diseased  tubers  which,  owing  to  mild  weather  or  protection 
from  frost,  do  not  decay  and  which  produce  volunteer  plant-  the  following  Spring. 

If  the  blight  ifl  due  to  the  dry-rot  fundus  (  Fuwirium  o.ryxj>oruin  >,  or  to  the  bai  I 

wilt  organism    Bacilhutolanaoearum  i,  the  land  should  not,  at  once,  be  need  for  pota- 

toes,  since  these  diseases  an-  harbored  from  year  to  year  in  the  soil. 

For  early  blight  a  satisfactory  answer  can  not  Ik-  given.      The  facts  are  not  known. 

XI.      lii.n.in-i'Kooi    Yakiki  : 

While  some  varieties  suffer  more  than  others  from  both  early  and  late  blight,  there 
are  none  entirely  blight  proof  and  probably  none  sufficiently  resistant  to  make  spray- 
ing Unnecessary.  Resistance  to  blight  is  a  desirable  quality  in  a  variety,  but  is  less 
Important  than  several  other  qualities.  Wherever  late  blight  occur-  potatoes  must 
be  sprayed  anyway,  and  consequently  the  slight  differences  in  the  blight  resistance 
of  the  different  varieties  do  not  amount  to  much.  Most  of  the  blight-proof  varieties 
advertised  are  humbugs 


REFERENCES. 

1.  For  a  more  extended  and  authoritative  discussion  of  early  blight  see  Vermont 
Sta.  Bui.  72,  pp.  16-25. 

2.  Vermont  Sta.  Buls.  49,  p.  98;  72,  p.  10. 

3.  Vermont  Sta.  Bui.  72,  p.  12. 

4.  U.  S.  Dept.  Agr.,  Farmers'  Bui.  91,  p.  10. 

5.  Vermont  Sta.  Bui.  49,  p.  97. 

6.  For  the  chemistry  of  Paris  green  see  U.  S.  Dept.  Agr.,  Farmers'  Bui.  146,  p.  7; 
California  Sta.  Bui.  151,  p.  3. 

7.  New  York  State  Sta.  Bui.  241,  p.  290. 

8.  U.  S.  Dept.  Agr.,  Report  for  1888,  pp.  337-339.  New  York  Cornell  Sta.  Bui. 
113,  pp.  249-254.  The  statement  (p.  250)  that  the  fungus  forms  oospores  is  an  error. 
New  Hampshire  Sta.  Bui.  22,  pp.  3-6.  Connecticut  Sta.  Rpt.  1904,  Part  IV,  pp. 
363-384;  same  for  1905,  Part  V,  pp.  304-330. 

9.  Vermont  Sta.  Bui.  49,  pp.  82-83. 

10.  New  York  State  Sta.  Bui.  241,  p.  289. 

11.  See  annual  reports  of  the  Vermont  Experiment  Station,  1891  to  1906. 

12.  U.  S.  Dept.  Agr.,  Div.  of  Veg.  Phys.  and  Path.  Bui.  12. 

13.  U.  S.  Dept.  Agr.,  Bureau  of  Plant  Industry  Bui.  55. 

14.  For  a  concise  resume  of  our  knowledge  of  scab  and  its  treatment  see  Vermont 
Sta.  Bui.  85. 

15.  Massachusetts  Sta.  Rpt.  1888,  pp.  131-138. 

16.  Connecticut  State  Sta.  Rpt.  1890,  pp.  81-95. 

17.  Indiana  Sta.  Bui.  39,  pp.  58-60. 

18.  For  a  general  account  of  Rhizoctonia  and  the  diseases  caused  by  it  see  New  York 
Cornell  Sta.  Bui.  186,  and  New  York  State  Sta.  Bui.  186.  A  discussion  of  the  potato 
Rhizoctonia  is  found  on  page  63  of  the  former  and  on  page  17  of  the  latter. 

19.  Ohio  Sta.  Bui.  139  contains  a  bibliography.     Ohio  Sta.  Bui.  145. 

20.  Colorado  Sta.  Buls.  70  and  91. 

21.  Minnesota  Sta.  Buls.  39,  pp.  212,  213;  45,  p.  310;  Illinois  Sta.  Bui.  40,  p.  138; 
New  York  State  Sta.  Bui.  101,  pp.  78-82. 

22.  Smith,  John  B.,  "  Economic  Entomology,"  pp.  225-228.  J.  B.  LippincottCo., 
Philadelphia,  1896.     Price,  $2.50. 

23.  Smith,  John  B.,  "Economic  Entomology,"  p.  219. 

24.  New  York  State  Sta.  Bui.  113. 

25.  The  best  work  in  this  country  on  potato  blight  and  its  treatment  has  been  done 
by  Prof.  L.  R.  Jones  at  the  Vermont  Experiment  Station.  Potato-spraying  experi- 
ments have  been  conducted  every  season  since  1890  and  the  subject  thoroughly  inves- 
tigated in  all  its  phases.  The  student  of  potato  spraying  should  not  fail  to  consult 
the  annual  reports  of  the  Vermont  Station  from  1890  to  date;  also  Bulletins  24,  28,  40, 
44,  49,  and  72. 

26.  Some  references  to  the  older  literature  of  potato  spraying  are  given  in  V.  B. 
Dept.  Agr.,  Div.  of  Veg.  Path.  Bui.  6,  p.  46. 

27.  New  York  State  Sta.  "bul.  101,  p.  74;  Vermont  Sta.  Rpt.  18,  p.  275. 

28.  Vermont  Sta.  Buls.  40,  pp.  25,  26;  44,  pp.  94-96. 

29.  New  York  State  Sta.  Bul  101,  p.  75. 

(29) 


30 

30.  Vennont  sta.  BoL  44,  p. 

31.  Frank,  B.,  Mid  Krfiger,  I  .  I  •  «  den  Reiz,  welchen  die  Behandlung  init 
Kupfer  auf  die  Kartofielpflanae  hervorbringt  Her.  d.  deotach.  boi.  GeeeUech. 
12,  pp.  B-ll;  New  York  state  Sta.  BoL  941,  pp.  878,  874. 

Vermont  sta.  P.ul.  72,  pp.  28 
Appendix,  I. 
84.  U.  >■  Dept.  Agr.,  Farmer-*  BoL  88,  p.  »'.     An  exhaustive  discussion  of  the 
chemical  and  physical  properties  of  Bordeanx  mixture  and  its  use  aa  a  fungicide  may 
be  found  in  U.  s.  Dept  Agr.,  I>iv.  of  Vagi  Phya.  and  Path.  Bole.  *j  and  9. 

.    35.   See  Appendix,  IV. 
See  Appendix,  VI. 
87.    Reported  by  F.  0.  BteWlH  et  al.  in  New  York  State  Bta.   Bui.  241,  pp.  27 
38.   New  York  State  Sta.  Bui.  123,  pp.  2:>>-245. 
Appendix,  IV. 

40.  See  Appendix,  VII I. 

41.  Rhode  Inland  Sta.  Buls.  26,  pp.  141-155;  30,  pp.  66-85;  33,  pp.  51-79;  40,  pp. 
80-96. 

42.  Pennsylvania  Dept.  Agr.  Bui.  105,  pp.  84,  85. 

43.  New  Jersey  Staa  Rpt.  1899,  p.  345;  New  Jersey  Stas.  Bui.  112;  Rhode  Island 
Sta.  Bui.  40,  pp.  87-95,  and  Vermont  Sta.  Bui.  85,  p.  lis. 

44.  Indiana  Sta.  Bui.  65. 

45.  The  corrosive  sublimate  treatment  for  potato  scab  originated  with  Prof.  H.  L. 
Bolley  of  the  North  Dakota  Experiment  Station*.  See  North  Dakota  Sta.  Buls.  4, 
pp.  11-14;  9,  pp.  27-33,  and  19,  pp.  131-134. 

46.  The  Vermont  Station  has  this  subject  under  investigation.     See  Buls.  115  and 
22;  also.  U.  S.  Dept.  Agr.,  Bu.  of  Plant  Indus.  Bui.  87  and  Ohio  Sta.  Bui.  174. 

O 


[Pot  Insertion  In  Farmers'  Institute  Lecture  X<>.  l\] 
ADDENDA. 

Since  this  syllabus  on  Potato  Diseases  and  Their  Treatment  was  written 
the  subject  hap  been  studied  more  completely.  It  has  been  found  necessary 
to  vary  the  treatment  of  some  of  the  diseases  enumerated  according  to  differ- 
ences in  local  conditions.  The  accompanying  notes  call  attention  to  some  of 
the  points  not  completely  covered  by  the  syllabus,  but  necessary  to  be  observed 
by  the  potato  grower,  depending  upon  his  location,  whether  in  the  South,  the 
irrigated  lands  of  the  West,  or  in  the  humid  climate  of  the  East  and  North. 

Experiments  are  in  progress  by  the  United  States  Department  of  Agriculture 
with  a  view  to  determining  more  accurately  the  efficacy  of  the  various  kinds 
of  treatment  prescribed.  When  these  experiments  have  been  completed  the 
syllabus  will  be  revised  to  conform  to  the  latest  information  on  this  subject. 
This  leaflet  contains  suggestions  made  by  W.  A.  Orton,  of  the  Bureau  of  Plant 
Industry,  and  is  inserted  with  a  view  to  adapting  the  teaching  to  the  special 
conditions  of  the  localities  in  which  the  instruction  is  given  pending  the  comple- 
tion of  the  investigations  now  in  progress. 

Early  blight. — In  the  South  and  West  the  term  "  early  blight "  is  often 
misleading,  as  the  AUerna/ria  leaf  spot  is  more  severe  on  the  southern  fall  crop 
than  on  the  spring  crop,  and  in  the  irrigated  sections  it  rarely  becomes  abun- 
dant until  late  in  the  fall.  In  either  case  the  profitableness  of  spraying  with 
Bordeaux  mixture  has  not  yet  been  adequately  demonstrated  by  experiments, 
and  can  not  be  as  confidently  recommended  as  in  the  North. 

Late  blight. — Date  blight  is  unknown  west  of  the  Great  Plains,  except  in 
limited  areas  on  the  Pacific  coast.  It  is  epidemic  in  the  South  only  on  the  early 
crop,  and  in  cool,  moist  seasons.    Refer  to  B.  P.  I.  Bull.  245. 

Scab.— Refer  also  to  B.  P.  I.  Circ.  23,  and  Me.  Expt.  Sta.  Bull.  141. 

Dry  rot. — Add  to  the  title  "  and  Wilt."  This  disease  is  proving  one  of  the 
most  widespread  and  serious  of  our  potato  troubles.  It  is  particularly  inju- 
rious in  the  Western  States,  where  it  is  a  serious  obstacle  to  potato  culture, 
except  where  a  systematic  rotation  of  crops  is  practiced.  It  is  becoming 
increasingly  prevalent  in  the  Central  and  Eastern  States.  In  many  cases  the 
disease  is  not  conspicuous,  as  the  vines  simply  appear  to  mature  early.  This 
early  death  of  the  foliage  and  the  resultant*  reduction  in  yield  constitutes  the 
greatest  loss  from  this  disease.  There  are  also  further  losses  from  decay  in 
storage  and  from  failure  to  germinate  when  diseased  tubers  are  planted. 
Rotation  of  crops  and  the  use  of  healthy  seed  are  the  only  means  of  control 
at  present  available.  Two  or  three  types  of  leaf -curl  diseases  appear  to  be 
confused  at  present.  Some  of  the  western  difficulties  often  attributed  to 
Fusarium  appear  to  be  associated  with  unfavorable  weather  and  cultural  con- 
ditions. * 

Rhizoctonia,  Rosette,  or  "  Little  potatoes." — This  disease  appears  in  west- 
ern irrigated  sections  to  be  associated  with  heavy  soils  deficient  in  organic 
matter.  In  many  localities  such  soils  can  not  be  profitably  used  for  planting 
potatoes.  The  lighter  types  may  be  improved  by  rotations  with  alfalfa  or  other 
green  manure  crops,  which  are  to  be  plowed  under  preceding  potatoes.  Rhi- 
zoctonia  is  seldom  a  serious  trouble  in  the  Eastern  States. 

Internal  browning. — This  disease  is  now  known  to  be  associated  with  a 
deficiency  in  the  available  supply  of  soil  moisture.  It  occurs  on  light  or 
droughty  soils  and  on  varieties  not  adapted  to  the  locality. 

The  following  new  diseases  should  be  mentioned : 

Black-leg  (Bacillus  phytophthorvs) . — This  is  characterized  by  the  blacken- 
ing of  the  lower  part  of  the  stem  when  the  potatoes  are  6  or  8  inches  high. 
The  leaves  yellow  and  curl  upward  and  inward  in  a  manner  characteristic  of 
this  disease.  Black-leg  is  commonest  in  eastern  trucking  districts.  As  a  rule 
it  occurs  only  to  a  slight  extent,  but  in  severe  cases  may  destroy  25  to  75  per 
cent  of  the  crop.  It  may  occur  also  in  epidemic  form  just  previous  to  harvest 
58843—12 


time,  causing  i  wn  rot  of  the  stems  and  tubers.  It  is  spread  on  or  in  the  seed 
tubers,  and  is  controllable  by  the  use  of  healthy  seed.  Refer  to  Me.  Bxpt 
Bta.  Bull.  174. 

Potato    wart    {Bynchitrimm    endoMoticum) .—Th  ae   is  prevalent   in 

limited  districts  in  Great  Britain  and  on  the  continent  of  Europe,  and  Is  charac- 
terised by   Irregular  warty  OUtgrOWthS  Starting  near  the  eyes.     These  lire  first 

white  or,  where  they  protrude  above  tin*  soil,  greenish  In  color,  later  becoming 
black  as  they  decay.     In  severe  cases  the  tubers  are  converted  into  unr< 
uizable  warty  masses,    it  is  a  dangerous  disease,  to  be  watched  for  and  rep 
wherever  observed,  In  order  thai  precautions  rnaj  be  taken  against  It*  further 

introductit.il  and  spread.    Refer  to  B.  P.  I.  Circ.  52  and  Farmers1  Bulletin  489. 
Ofkki  oi   Experiment  Statioh 

Washington,  D.  C,  July  1,  1912. 


I 


